Installation and test tool for ionization smoke detector

ABSTRACT

In the present invention a ceiling mounted smoke detector assembly has a permanently mounted ceiling fixture portion and a detachably mounted smoke detector head adapted for mounting to the fixture portion. To provide for ease of installation, removal, and/or testing of the smoke detector head or of testing the entire assembly there is an installation and testing tool which mechanically and electrically interlocks with the smoke detector head.

United States Patent Larsen et al.

INSTALLATION AND TEST TOOL FOR IONIZATION SMOKE DETECTOR inventors: Larry D. Larsen, Palatine; Lee

Schuck, Buffalo Grove; Joseph C. Pekarek, Mt. Prospect; Richard C. Mott, Harwood Heights. all of Ill.

Assignee: Honeywell Inc.. Minneapolis, Minn.

Filed: Aug. 15. 1973 App]. No.: 388,520

U.S. Cl 324/l58 R; 81/3 R; 340/237 Int. Cl. G0ln 23/12; B2Sb 27/00 Field of Search 8l/3 R; 324/l58 R;

References Cited UNlTED STATES PATENTS Wilson 81/3 R Aug. 19, 1975 Johnson et all 81/3 R X Lumpart et ai 340/237 5 X Prinmry Zitamtner-Alfred E. Smith Assistant Examiner-Rolf Hille Attorney, Agent, or Firm-Omund R. Dahle [57] ABSTRACT In the present invention a ceiling mounted smoke detector assembly has a permanently mounted ceiling fixture portion and a detachably mounted smoke detector head adapted for mounting to the fixture portion. To provide for ease of installation, removal, andlor testing of the smoke detector head or of testing the entire assembly there is an installation and testing tool which mechanically and electrically interlocks with the smoke detector head.

12 Claims, 7 Drawing Figures PATENTED AUG] 91975 SHEET 1 BF PATENTEIW 9975 3, 900, 795

I SHEET 2 OF 4 INSTALLATION AND TEST TOOL FOR IONIZATION SMOKE DETECTOR BACKGROUND AND SUMMARY OF THE INVENTION The mounting of smoke detectors at the ceiling level of an area being protected is a normal placement. In a large building or building complex the number of detectors used is large and may run into the hundreds of units. In the past many of these detectors have not been easily installed. removed, replaced. adjusted and/or tested by a person standing on the floor below the detector. It has generally been necessary to bring in a ladder, or the like, to reach each detector since they are normally out of reach. In addition, in many buildings the use of suspended ceilings is in vogue wherein loose lay-in ceiling panels are suspended on a metal grid frame. These panels are usually 2 X 4 feet in size and relatively light in weight. To these lay-in panels the smoke detectors are mounted.

In the smoke detectors known to applicants up to the present time. there have been two piece units having a permanently mounted ceiling fixture portion and a detachably mounted smoke detector together with an in stallation tool, however, the assembly requires an upward insertion force for the smoke detector portion to latch with the ceiling fixture portion. The loose ceiling panels of the suspended ceilings do not resist upward pressure so that ceiling fixture and ceiling panel have a tendency to move upward with the smoke detector as an insertion attempt is made and such an arrangement is not entirely satisfactory. In the present invention the smoke detector head and ceiling fixture portion are so designed that no vertical insertion force is required to engage and lock the smoke detector head in place and therefore the smoke detector may easily be installed or removed from the ceiling fixture and/or tested with the installation and testing tool by one standing on the floor below the assembly. The installation and testing tool mechanically and electrically connects to the smoke detector head for installing and removing smoke detectors from the ceiling fixtures and also provides electrical connection between the detector test points and a test set.

To accomplish this the tool is connected to the smoke detector head by inserting the L-shaped probes into the circular slot of the smoke detector head and rotating the tool until the probes contact the printed circuit test point tabs. Additional shaft or handle rotation of the tool with respect to the head causes a cam to raise and lock the tool onto the test point tabs. In the locked position the tool and smoke detector head become, in effect. a single unit. In the locked position the installation tool may be left hanging on the smoke detector assembly. Also. in the locked position the detector head may be removed from the ceiling fixture by turning the tool handle counterclockwise. and may be inserted into the ceiling fixture by rotating the tool handle clockwise. The tool is unlocked from the head by pulling downward slightly on the handle of the tool and rotating it clockwise whereupon the locking mechanism snaps back to the original open or unlocked position. The tool is then rotated counterclockwise to disengage the probes from the circular slot of the detector head and the tool is then withdrawn. The printed circuit test point tabs have thereon a number of smoke detector test terminals which mate with spring contacts on the test tool thereby providing electrical connection from a number of points of the smoke detector head circuit to the test set.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an exploded view in perspective of the smoke detector mounting and testing tool, the smoke detector head. and the permanently mounted ceiling fixture portion;

FIG. 2 is a perspective view of the installation and testing tool in a first position wherein it is ready to engage a smoke detector head;

FIG. 3 is a perspective view of the installation and testing tool in a locked position wherein the tool is locked onto the smoke detector head;

FIG. 4 is a somewhat simplified view of the reverse side of the smoke detector head;

FIG. 5 is a partial cross-sectional view of a portion of FIG. 4.

FIG. 6 is a detailed view of an electrical contact and locking component of the fixture portion; and,

FIG. 7 is a schematic drawing of a smoke detector and the Test Set.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 there is disclosed an exploded perspective view of a smoke detector installation and testing tool It) and a smoke detector assembly II comprising a detachable smoke detector head 12 and a ceiling fixture portion I3 to be permanently mounted and wired. The three components 10, I2 and 13 which cooperate together are shown in axial alignment but separated for ease of explanation.

The ceiling fixture 13 of the assembly II is intended to be permanently mounted to the ceiling by mounting holes 14 and wired to a central panel. not shown. Large numbers of smoke detector assemblies II may be connected to the central panel. The fixture I3 includes a plurality of fixed electrical contacts 15 affixed thereon of which only two have been shown in detail. In one specific embodiment of the invention there are six such contacts, several of which are slightly modified as in FIG. 6 to include at one end thereof a laterally offset bayonet type latching tab I6. An arcuate bar 17 of the fixture 13 is a positioning guide for the sensor head 12 and the keyways 20 and 21 of the arcuate bar 17 cause the detector head I2 to be received in the proper orientation.

The smoke detector head 12 is generally disc shaped or saucer shaped and on the exposed surface has a raised slotted pillbox portion 22 enclosing the smoke sensing chamber. An annular or circular slot 23 in the face of the detector head is adapted to receive and guide probes of the tool 10. Extending into the space of the slot are opposite end tabs 24 and 25 of the printed circuit board, these tabs 24 and 25 being known as the printed circuit test point tabs. Each tab has a plurality of test points shown as pads 26, 27, 28, 30, 31 and 32. These test point tabs 24 and 25 act as handles to be grasped by the installation and testing tool 10.

The reverse side of the detector head I2 is shown in FIG. 4. The circular area 33 fits within and mates with the circular bar 17 of fixture I3 and the keys 34 and 35 cooperate with keyways 20 and 21 respectively to properly orient the detector head 12 when it is desired to engage and lock the head in place. Bayonet type latching slots 36, 37 and 38 in the head I2 each have a widened slot portion 40 allowing the laterally offset latching tabs 16 to pass through. The sensing head is then rotated clockwise to lock it in place on the latching tabs I6. FIG. 4 also discloses a plurality of resilient cammed contacts 41 which mate with the fixed contacts 15 of the fixture 13. An edge view of these resilient cammed contacts 41 is shown in FIG. 5 and it can be seen that the contact 41 extends through a rectangular opening in the circular area 33 in such a way that the leading edge or end 42 of the resilient contact surface is substantially lower than the opposite end 43. At the position of insertion of detector head 12 into fixture 13 the fixed contacts I5 align with the lower edge 42 of the contacts 41 respectively. No insertion pressure is required for this insertion as the resilient contacts are not loaded in this insertion position. As the detector head 12 is rotated to lock it in place, the resilient contacts 4] are wiped by contacts from edge 42 to edge 43 and progressively pick up more loading in the process. When the detector head is fully locked in place the resilient contacts 41 may be depressed by the loading as shown in phantom by FIG. 5.

The installation and testing tool 10 as shown in FIGS. 1, 2 and 3 comprises a shaft or handle 50 which may be of any convenient length for an operator to reach the ceiling of the area with the tool. The upper end of the shaft is non-rigidly affixed by a spline type coupling to a transversely mounted arm 51 which has at the edges thereof a pair of ramp like cam surfaces 52 and 53. The cam carrying arm 51 rotates together with the shaft 50.

A second section of tool 10 is a rigid latching bracket 55 or base member means which is rotatably mounted on shaft 50. Bracket 55 includes a pair of vertically positioned L-shaped smoke detector head engaging fingers 56 and 57 which extend sufficiently to reach into the circular slot 23 and mechanically engage behind printed circuit tabs 24 and 25. A spring 60 urges shaft 50 upwardly with respect to bracket 55 so that pin 61 abuts surface 62 of bracket 55. Bracket 55 also has a locking notch 63 into which pin 61 drops in the locked position as shown in FIG. 3.

A third section of tool 10 is a spring-loaded test probe assembly 65 comprising a generally planar base section 66 having mounted thereon pin housings 67 and 68 containing spring loaded test probes or pins 70-75. The assembly 65 also includes locking fingers 76 and 77 which prevent printed circuit tabs 24 and from slipping out of position when the tool is in the locked position as shown in FIG. 3. Spring members 80 and 8] tend to keep assembly 65 downwardly towards the unlocked or open position as shown in FIGS. 1 and 2.

In addition to the mechanical arrangement of the installation and testing tool which has been described, not shown in FIGS. 1-6 are a multiconductor cable which extends from a test set to a connector which mounts in connector socket 82 of bracket 55. Also not shown are the wires or cable from individual test pins 70-75 to the connector. FIGS. 2 and 3 have been simplified to the extent of not showing the connector socket 82.

FIG. 7 is a schematic representation of the electrical circuit of the smoke detector. the interconnecting cable and the test set. The details of the smoke detector circuit are described in detail in the copending application of Larsen and Kobek Serial No. 376.0l l, entitled Smoke Detector Circuit," filed July 2, i973, and assigned to the same assignee, now US Pat. No. 3.8 I 2,362. Reference may be had to that case for a detailed description. Suffice it to say that the smoke detector is an ionization type smoke detector which provides two outputs. one being an analogue voltage output at point 31 which voltage deviates from a clean air voltage as a function of the smoke density being sensed. The other output is a switched output at point 27 which indicates by switching that a predetermined smoke level has been exceeded. This switching is done by a comparator switching circuit. The smoke detector is to be used in a system not here shown. The test terminals 26, 27, 28, 30, 3t, 32 are the printed circuit board test points of the same number shown in FIG. 1.

FIG. 7 shows schematically the test probe pins -75 of tool I0 and a flexible multiconductor cable 83 which interconnects the test probe pins to the test set 84. Conductors 70'. 71', 72', 73'. 74' and of the test set correspond to test probe pins 70-75, respectively. The test set includes a first two level rotary wafer switch S2 which has a first rotary contact 85 which selectively contacts fixed contacts a. b. c. d and e. of which the last 0 is not used, and which has a second rotary contact 86, ganged to the first contact 85, which likewise contacts fixed contacts a. h, c. (1'. and e of which only the last 2 is used. The conductors 7| 72', 74' and 75' are directly connected to fixed contacts a. h, t, and d respectively. The conductor 70' is directly connected to fixed contact e.

The test set includes a second two level rotary wafer switch S2 which has a first rotary contact which selectively contacts fixed contactsf. g. I: and i, and which has a second rotary contact 91, ganged to contact 90, which likewise contacts fixed contacts j', g. h and 1''. Fixed contacts j". g and 1' are directly connected to ground conductor 73'. Contact 1' is connected by a resistor 92 to the conductor 7], the conductor 71' also being connected by an alarm lamp 93 to the rotary contact 86. The rotary contacts 90 and 91 of switch 52 connect to the terminals of a meter 94. Associated with switch 52 are a pair of transistors 95 and 96 connected in an emitter follower configuration. The base of transistor 95 is directly connected to conductor 72' and the emitter is connected by a load resistor 97 to conductor 73' and by resistors 98 and 99 to fixed contacts g and ii. The base of transistor 96 is connected to conductor 74' and the emitter is connected to contacts f and I2 and by a load resistor 100 to conductor 73.

The system wiring to the smoke detector provides a B voltage to conductor 70 and ground potential on conductor 73' of the test set thus powering the test set when the smoke detector head is installed, the system power is on and the test tool 10 is locked onto the installed head. If the system power is off, the power to run the test set is supplied by internal batteries I01 connected across terminals 70 and 73'. An on-off switch S4 and a diode is also in this internal battery circuit. A normally open Test switch S1 is connected from conductor 70 to conductor 75'. A normally open Resef switch S3 is connected from conductor 70' to conductor 72.

The test set 84 includes a comparator section Ill) which is energized from the 8* line 70' and which has a signal input conductor I II connected to rotary contact 85 of switch S6. Conductor 11] connects to one output terminal 112 of a resistive bridge circuit which bridge is energized from line 70'. The bridge comprises resistors I13, 114, 115, I16 and 117. The bridge also has output terminals 120 and 121 which provide fixed bias voltages, the voltage at terminal I12 being controlled by the voltage picked up on rotary contact 85 except in position e.

The comparator section I also includes two lC amplifiers 122 and 123 which may be type 741's. Bridge output terminals 120 and 121 are connected to the negative (inverting) input of amplifier 122 and the positive (non inverting) input of amplifier 132, respectively. Bridge output terminal 1 I2 is connected to the positive input of amplifier 122 and to the negative input of amplifier 123. The output terminals of amplifiers 122 and 123 are connected to the contact electrodes of transistors 124 and 125, respectively, and turn on the transis tor when the amplifier output is positive, the transistors 124 and I having indicator lamp L1 and L2 in their collector load circuit.

OPERATION The legend of FIG. 7 indicates how a number of checks and measurements can be made with the test set 84 on the smoke detector head 12 whether or not it is installed in the ceiling fixture 13. Let it first be assumed that the tool 10 and the smoke detector head 12 are locked together and that it is desired to test the detector head prior to installation in a ceiling fixture. The test battery 10] provides the necessary power for the detector head and the test set. Considering first the switch S2 and the indicating meter 84 which are used in test of the detector head. During this test the switch S6 should be in the 6 position which, as indicated in the legend is the detector test position. By rotating the switch S2 through the positionsf, I1 and i the voltages which may be read on the meter 94 in order are the an alogue voltage at terminal 31, the set point voltage at terminal 28, the voltage and differential between the set point and the analogue voltage, and the voltage at the detector output terminal 27. The same test can be made on the smoke detector head when it is installed in the ceiling fixture l3 and operating from system power.

The test set 84 is also designed to test the field wiring interconnecting ceiling fixture l3 and a cental station. The selector switch S6 and a comparator circuit 110 with indicating lamps L] and L2 is used for this test. As pointed out by the legend, the positioning of switch arm 85 at positions a, h, c or d provides test of the alarm wiring, set point wiring, the analogue wiring, and the test wiring. A high positive voltage on input lead 111 causes lamp L1 to glow while a lower ground potential on the input lead causes the lamp L2 to glow. If an erroneous voltage is discovered during this test the switch S5 can be actuated to determine whether the voltage being sensed is AC or DC.

During the test of the smoke detectors and particularly in switch position 521', a smoke condition can be simulated by the switch 81 which causes the switch in the smoke detector to turn on and short to ground the terminal 27. The reset switch S3 can be then depressed when it is desired to reestablish the initial standby condition of the smoke detector. A voltage on meter 94 will indicate the switching and the reset.

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. In a smoke detector system an installing and testing tool mechanically and electrically cooperating and interlocking with a smoke detector device, the system comprising in combination:

a smoke detector device having a permanently mounted overhead fixture portion with a plurality of electrical contacts which are adapted to be wired to a central station, and said device having a detachably mounted smoke sensor portion adapted for mounting to said fixture portion, said smoke sensor portion including a plurality of electrical contacts positioned to match with the contacts of the fixture portion,

said smoke sensor portion having a pair of tabs with electrical test terminals thereon, said tabs being adapted to engage and be grasped by an installing and testing tool;

an installing and testing tool for said smoke sensor portion, said tool having tab engaging and grasping means, said last named means including test probe finger means positioned to make contact with said electrical test terminals on said tabs when said tabs are engaged and grasped by said tool, and

said tool having extended handle means which is rotationally operative to cause said tab engaging and grasping means to grasp and release said tabs.

2. The invention according to claim 1 and further comprising:

said tool including an electrical source for energizing said smoke sensor portion by way of said electrical test terminals, said tool and smoke sensor portion providing an independently operative and portable smoke sensor.

3. The invention according to claim I and further comprising:

said tool having meter means and circuit means connecting said meter means to said test probe finger means.

4. The invention of claim I wherein said smoke sensor tabs are a portion of a printed circuit board on which board the electronic circuit of the smoke sensor.

5. The invention of claim 1 wherein said tool tab engaging and grasping means further includes a pair of L- shaped extended fingers adapted to reach behind said smoke sensor tabs.

6. The invention according to claim 1 wherein the smoke detector device further comprises insert-androtate-tolock bayonet type fastening means on said two device portions for mounting and securing said smoke sensor portion to said fixture portion, said fastening means having no spring loading during insertion to present no resistance to insertion; and wherein at least a portion of the electrical contacts of said smoke detector device are resilient and provide a spring loading on one device portion relative to the other upon rotation-to'lock said smoke sensor portion to said fixture portion.

7. An installing and testing tool for use with a detachably mounted smoke detector device, the tool comprising in combination:

base member means including thereon a plurality of extended smoke detector device engaging fingers and test probe finger means cooperating with said extended engaging fingers, the engaging fingers and the test probe finger means being adjustable one relative to the other and adapted for engaging and interlocking with tabs of a smoke detector device; and,

handle means rotatably mounted to said base member means, and cam means connected to said handle means and positioned together with said base member means and rotatable by said handle means to cause said test probe finger means and said smoke detector engaging fingers to move one relative to the other when said handle means is being rotated with respect to said base member means.

8. The invention of claim 7 wherein said test probe finger means provide electrical contact from test points on the tabs of a smoke detector device through a multiconductor cable to a test set.

9. The invention of claim 7 and further comprising:

battery powered Test set means including multiconductor cable means eletrically connected to said test probe finger means so that operational tests can be made on a smoke detector device. 10. A method of installing and testing smoke detector heads into ceiling fixtures using an installation and testing tool comprising the steps of:

inserting smoke detector tab grasping means of an installation and testing tool into a smoke detector head and rotating said tool in a first direction until the tab grasping means contact the smoke detector tabs; rotating further in the first direction the handle of the tool with respect to the smoke detector head to lock together the tool and smoke detector head;

inserting the tool mounted smoke detector head into ceiling fixture;

rotating the tool and smoke detector head in the first direction to lock the smoke detector head into the ceiling fixture;

rotating still further in the first direction the handle of the tool with respect to the now installed smoke detector head to unlock the tool from the smoke detector head;

rotating tool in the opposite direction until the tab grasping means are clear of the smoke detector tabs and withdrawing the tool from the installed smoke detector head.

H. in a smoke detector system an installing and testing tool mechanically and electrically cooperating and interlocking with a smoke detector device having a permanently mounted overhead fixture portion with a plurality of electrical contacts which are adapted to be wired to a central station, and said device having a detachably mounted smoke sensor portion adapted for mounting to said fixture portion, said smoke sensor portion including a plurality of electrical contacts positioned to match with the contacts of the fixture portion, said smoke sensor portion having a pair of tabs with electrical test terminals thereon, said tabs being adapted to engage and be grasped by an installing and testing tool;

the installing and testing tool comprising:

an installing and testing tool for said smoke sensor portion, said tool having tab engaging and grasping means, said last named means including test probe finger means positioned to make contact with said electrical test terminals on said tabs when said tabs are engaged and grasped by said tool, and

said tool having extended handle means which is rotationally operative to cause said tab engaging and grasping means to grasp and release said tabs.

12. The method of claim 10 and comprising the additional step of:

testing said smoke detector head while said tool and smoke detector head are locked together. 

1. In a smoke detector system an installing and testing tool mechanically and electrically cooperating and interlocking with a smoke detector device, the system comprising in combination: a smoke detector device having a permanently mounted overhead fixture portion with a plurality of electrical contacts which are adapted to be wired to a central station, and said device having a detachably mounted smoked sensor portion adapted for mounting to said fixture portion, said smoke sensor portion including a plurality of electrical contacts positioned to match with the contacts of the fixture portion, said smoke sensor portion having a pair of tabs with electrical test terminals thereon, said tabs being adapted to engage and be grasped by an installing and testing tool; an installing and testing tool for said smoke sensor portion, said tool having tab engaging and grasping means, said last named means including test probe finger means positioned to make contact with said electrical test terminals on said tabs when said tabs are engaged and grasped by said tool, and said tool having extended handle means which is rotationally operative to cause said tab engaging and grasping means to grasp and release said tabs.
 2. The invention according to claim 1 and further comprising: said tool including an electrical source for energizing said smoke sensor portion by wAy of said electrical test terminals, said tool and smoke sensor portion providing an independently operative and portable smoke sensor.
 3. The invention according to claim 1 and further comprising: said tool having meter means and circuit means connecting said meter means to said test probe finger means.
 4. The invention of claim 1 wherein said smoke sensor tabs are a portion of a printed circuit board on which board the electronic circuit of the smoke sensor.
 5. The invention of claim 1 wherein said tool tab engaging and grasping means further includes a pair of L-shaped extended fingers adapted to reach behind said smoke sensor tabs.
 6. The invention according to claim 1 wherein the smoke detector device further comprises insert-and-rotate-to-lock bayonet type fastening means on said two device portions for mounting and securing said smoke sensor portion to said fixture portion, said fastening means having no spring loading during insertion to present no resistance to insertion; and wherein at least a portion of the electrical contacts of said smoke detector device are resilient and provide a spring loading on one device portion relative to the other upon rotation-to-lock said smoke sensor portion to said fixture portion.
 7. An installing and testing tool for use with a detachably mounted smoke detector device, the tool comprising in combination: base member means including thereon a plurality of extended smoke detector device engaging fingers and test probe finger means cooperating with said extended engaging fingers, the engaging fingers and the test probe finger means being adjustable one relative to the other and adapted for engaging and interlocking with tabs of a smoke detector device; and, handle means rotatably mounted to said base member means, and cam means connected to said handle means and positioned together with said base member means and rotatable by said handle means to cause said test probe finger means and said smoke detector engaging fingers to move one relative to the other when said handle means is being rotated with respect to said base member means.
 8. The invention of claim 7 wherein said test probe finger means provide electrical contact from test points on the tabs of a smoke detector device through a multiconductor cable to a test set.
 9. The invention of claim 7 and further comprising: battery powered Test set means including multiconductor cable means eletrically connected to said test probe finger means so that operational tests can be made on a smoke detector device.
 10. A method of installing and testing smoke detector heads into ceiling fixtures using an installation and testing tool comprising the steps of: inserting smoke detector tab grasping means of an installation and testing tool into a smoke detector head and rotating said tool in a first direction until the tab grasping means contact the smoke detector tabs; rotating further in the first direction the handle of the tool with respect to the smoke detector head to lock together the tool and smoke detector head; inserting the tool mounted smoke detector head into ceiling fixture; rotating the tool and smoke detector head in the first direction to lock the smoke detector head into the ceiling fixture; rotating still further in the first direction the handle of the tool with respect to the now installed smoke detector head to unlock the tool from the smoke detector head; rotating tool in the opposite direction until the tab grasping means are clear of the smoke detector tabs and withdrawing the tool from the installed smoke detector head.
 11. In a smoke detector system an installing and testing tool mechanically and electrically cooperating and interlocking with a smoke detector device having a permanently mounted overhead fixture portion with a plurality of electrical contacts which are adapted to be wired to a central station, and said device having a detachably mounted smoke sensor portion adapted for mOunting to said fixture portion, said smoke sensor portion including a plurality of electrical contacts positioned to match with the contacts of the fixture portion, said smoke sensor portion having a pair of tabs with electrical test terminals thereon, said tabs being adapted to engage and be grasped by an installing and testing tool; the installing and testing tool comprising: an installing and testing tool for said smoke sensor portion, said tool having tab engaging and grasping means, said last named means including test probe finger means positioned to make contact with said electrical test terminals on said tabs when said tabs are engaged and grasped by said tool, and said tool having extended handle means which is rotationally operative to cause said tab engaging and grasping means to grasp and release said tabs.
 12. The method of claim 10 and comprising the additional step of: testing said smoke detector head while said tool and smoke detector head are locked together. 